Variations in High-frequency Oscillations of Tropical Cyclones over the Western North Pacific
Variations in the high-frequency oscillations of tropical cyclones (TCs) over the western North Pacific (WNP) are studied in numerical model simulations. Power spectrum analysis of maximum wind speeds at 10 m (MWS10) from an ensemble of 15 simulated TCs shows that oscillations are significant for all TCs. The magnitudes of oscillations in MWS10 are similar in the WNP and South China Sea (SCS); however, the mean of the averaged significant periods in the SCS (1.93 h) is shorter than that in the open water of the WNP (2.83 h). The shorter period in the SCS is examined through an ensemble of simulations, and a case simulation as well as a sensitivity experiment in which the continent is replaced by ocean for Typhoon Hagupit (2008). The analysis of the convergence efficiency within the boundary layer suggests that the shorter periods in the SCS are possibly due to the stronger terrain effect, which intensifies convergence through greater friction. The enhanced convergence strengthens the disturbance of the gradient and thermal wind balances, and then contributes to the shorter oscillation periods in the SCS.
Key wordstropical cyclone high-frequency oscillation western North Pacific South China Sea
本文通过数值模拟研究了西北太平洋(WNP)热带气旋(TC)高频振荡的一些特征. 通过对15个集合模拟TC的中心附近最大10米风速(MWS)的功率谱分析, 所有TC的高频振荡显著, 振荡周期相近. 然而, 在南海(SCS)的振荡周期(平均1.93小时)则显著短于活动在西北太平洋开阔海域TC的振荡周期(平均2.83小时). 通过分析集合模拟的模式输出结果, 和对“黑格比”(2008)的个例模拟及其数值敏感试验(试验中所有陆地被替换为海洋), 得出在南海区域, 由于陆地分布较多, 引起TC边界层摩擦辐合较强. 强的摩擦辐合增加了TC边界层的不稳定因素, 引起了南海区域TC高频振荡周期缩短.
关键词热带气旋 高频振荡 西北太平洋 南海
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This work was supported by the National Natural Science Foundation of China (Grant Nos. 41405048, 41675043, 41375050, 41205032 and 41775094) and Independent Research Project Program of State Key Laboratory of Tropical Oceanography (Grant No. LTOZZ1603). We are grateful for the use of the Tianhe-2 supercomputer (National Supercomputer Center in Guangzhou, Sun Yat-Sen University) and the HPCC (South China Sea Institute of Oceanology, Chinese Academy of Sciences), which were used in all numerical simulations. The authors would like to thank the three anonymous reviewers for their comments to improve the paper.
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